Polymorphism of 4-bromobenzophenone

Abstract

A combination of single-crystal and powder X-ray diffractometry was used to study the structure of two polymorphs of 4-bromobenzophenone over the temperature range from 100 to 300 K. One of the polymorphs of the title compound was known previously and its structure has been determined at room temperature [Ebbinghaus et al. (1997). Z. Kristallogr. 212, 339-340]. Two crystal growth methods were employed, one of which (a modification of the Bridgman-Stockbarger technique) resulted in single crystals of a previously unknown structure. The basic physical properties of the stable polymorph are: growth method, from 2-propanol solutions or gradient sublimation; space group, monoclinic P2(1)/c; melting point, T(m) = 355.2 K; X-ray density (at 100 K), D(x) = 1.646 g cm(-3). The same properties of the metastable polymorph (triclinic P\overline 1 ) are: growth method, modified Bridgman-Stockbarger method; X-ray density (at 100 K), D(x) = 1.645 g cm(-3); T(m) = 354 K. Thermograms suggest that the melting of the metastable form is accompanied by at least a partial crystallization presumably into the monoclinic form; the transformation is therefore monotropic. Analysis of short distances in both polymorphs shows that numerous weak hydrogen bonds of the C-H...pi type ensure additional stabilization within the respective planes normal to the longest dimension of the molecules. The strong temperature dependence of the lattice constants and of the weak bond distances in the monoclinic form suggest that the weak bond interactions might be responsible for both the large thermal expansion within plane bc and the considerable thermal expansion anisotropy.

Uniaxial Negative Thermal Expansion in Polymorphic 2-Bromobenzophenone, Due to Aromatic Interactions?

“…This entails that the large electronegativity of the Br substituent leads to a strong molecular asymmetry which suppresses the energy gain of cross-conjugation between the two aryl moieties, leading to a coplanar geometry that maximizes electron delocalization between the carbonyl group and the unsubstituted ring. A survey of other mono-substituted analogues (Figure 1), such as 2-chlorobenzophenone (2-ClBPh), 19 4-bromobenzophenone (4-BrBPh), 20 or 4-methylbenzophenone (4-methylBPh) 14 for which crystal structures of the stable and metastable phases have been described, shows that the interplay between chirality, the structures, and their stability is highly unpredictable. Whereas stable phases of 4-methylBPh (P21/c), 2-ClBPh (P21/c) and 4-BrBPh (P21/c) are centrosymmetric (racemic) crystal structures, metastable phases (when they have been discovered) were found either to contain both enantiomers, i.e.…”

“…A survey of other monosubstituted analogues (Figure ), such as 2-chlorobenzophenone (2-ClBPh), 4-bromobenzophenone (4-BrBPh), or 4-methylbenzophenone (4-methylBPh) for which crystal structures of the stable and metastable phases have been described, shows that the interplay between chirality, the structures, and their stability is highly unpredictable. Whereas stable phases of 4-methylBPh ( P 2 1 / c ), 2-ClBPh ( P 2 1 / c ) and 4-BrBPh ( P 2 1 / c ) are centrosymmetric (racemic) crystal structures, metastable phases (when they have been discovered) were found either to contain both enantiomers, i.e., to be racemic crystals, in the case of 4-BrBPh with a P 1̅ space group, or to contain only one enantiomer, i.e., to be enantiomorph crystals, in the case of 4-methylBPh with a P 3 1 space group.…”

Polymorphism and Solvatomorphism 2007

“…Besides the papers just discussed, the 2007 literature contained a large number of additional reports on the polymorphism associated with a wide variety of organic compounds. While some of these substances may be of limited pharmaceutical interest, the reported results77–124 are summarized in Table 1 for those workers who may have a suitably directed interest.…”

Role of Optical Phonons and Anharmonicity in the Appearance of the Heat Capacity Boson Peak-like Anomaly in Fully Ordered Molecular Crystals

“…These bromine-benzophenones (C 13 H 9 OBr) are isomers that differ in the position (2, 3, and 4, respectively) of the Br atom in one of the phenyl rings ( o -, m - and p -bromobenzophenone, respectively). The polymorphism of these materials has been extensively studied by using different experimental techniques − (see the Supporting Information for details). For the particular case of 4-BrBZP, we have analyzed the stable monoclinic crystalline phase [4-BrBZP­(M)] and a metastable triclinic polymorph [4-BrBZP­(T)] that can be supercooled to the lowest temperature considered here.…”